The present proposal seeks to understand how fear maps into behavior from a functional perspective. In addition, it seeks to uncover mechanisms that underlie the performance of such fear motivated behavior. In order to survive, animals must be able to react to a variety of environmental dangers with swift but effective patterns of defensive behavior. The animal may react with any one of a variety of motor behaviors such as changes in feeding pattern, freezing, or vigorous escape, with the particular behavior selected being a function of the degree of threat. Besides motor behaviors the fear reaction is accompanied by autonomic modulation and analgesia that support the motor behaviors. This coordination of environmental stimuli and behavior serving the function of defense against environmental dangers is referred to as the defensive behavior system. Within this framework, fear and anxiety are convenient labels to refer to the activation of this functional behavior system. Obviously, this elaborate orchestration of stimuli and responses must be performed by an efficient and well integrated neural circuitry. The evidence reviewed suggests that the periaqueductal gray matter is in an ideal position to coordinate these various response components with the degree of threat. The experiments proposed in this grant application are designed to build on this relationship of the PAG to the organization of defensive behavior and also to further develop our knowledge of the organization of defensive behavior in response to manipulations of relevant environmental variables. The experiments described attempt to determine how differing levels of fear map into different modes of behavioral action. We will attempt to find the brain sites corresponding to performance of conditional and unconditional defensive responses to further clarify how these responses interact. It will be determined if activity in these brain regions is necessary and sufficient for performance fear of related defensive behaviors and particular attention will be paid to the separation of learning and performance factors. We will also conduct an analysis of the mechanisms responsible for conditional fear mediated by emotional as opposed to representational associations.